This invention relates to a fuel injection equipment for an internal combustion engine, and more particularly to a fuel injection equipment for feeding an internal combustion engine with fuel.
A fuel injection equipment for an internal combustion engine which has been conventionally used in the art, as shown in FIG. 5, generally includes an injector 1, a fuel injection command signal generation section 2, an injector driving circuit 3 and a power supply 4.
The injector 1, as shown in, for example, FIG. 6, includes a valve body 1b provided at a distal end thereof with a fuel injection port 1a a valve 1c including a valve seat 1c1 formed in an inner end of the fuel injection port 1a and a needle 1c2 arranged in the valve body 1b and operating the fuel injection port 1a, an electromagnet 1f including a plunger 1d connected to the needle 1c2 and an exciting coil 1e and openably actuating the valve 1c, and a return spring 1g for urging the plunger 1d to hold the valve 1c at a closed position. The valve body 1b is provided on a rear end side thereof with a fuel feed port 1h, which is connected to a fuel pump (not shown), so that fuel F is fed from the fuel pump through the fuel feed port 1h to the valve body 1b and therefor the injector 1 under a predetermined fuel feed pressure P.
In the injector 1 thus constructed, when a driving voltage is applied across the exciting coil 1e to feed an exciting current Id thereto, the plunger 1d is retracted into the exciting coil 1e, resulting in the valve 1c being actuated to open the fuel injection port 1a. The valve 1c is kept open until the electromagnet 1f is de-energized, during which fuel is outwardly ejected through the fuel injection port 1a.
The injection command signal generation section 2 comprises a microcomputer including, for example, a CPU, a ROM, a RAM and the like and is fed with an output of a signal source 5 for generating a signal containing information on a rotation angle of an internal combustion engine and that on an engine speed of the engine, as well as an output of various sensors 6 such as a temperature sensor, an atmospheric pressure sensor, a sensor for detecting a degree of opening of a throttle and the like, to thereby operate a fuel injection start position .theta.j and a signal width Tj of an injection command signal required for ejecting predetermined fuel, resulting in generating an injection command signal Vj of a rectangular waveform having the signal width Tj at the fuel injection start position .theta.j thus operated.
The injector driving circuit 3 functions to flow an exciting current Id through the exciting coil 1e of the injector 1 during a period of time for which the injection command signal Vj is generated. For this purpose, the injector driving circuit 3 includes a switch circuit 3a constituted by a semiconductor element such as a transistor Tr or the like. The switch circuit 3a is connected in series to the exciting coil 1e of the injector 1, so that the diving voltage Vd generated from the power supply 4 may be applied through a resistor 7 across a serial circuit constituted by the exciting coil 1e and switch circuit 3a.
In the conventional fuel injection equipment constructed as described above, when the injection command signal generation section 2 generates an injection command signal Vj, the switch circuit 3a of the injector driving circuit 3 is caused to be turned on to flow an exciting current Id through the exciting coil 1e of the injector 1. FIG. 7 shows a variation in exciting current Id to time t, wherein curves a and b indicate characteristics obtained when the driving voltage Vd is Vd1 and Vd2 (&lt;Vd1), respectively. Also, in FIG. 7, t1 indicates time at which the valve of the injector is rendered open when the driving voltage Vd is Vd1 and t2 indicates time at which the valve is open when the voltage Vd is Vd2.
As will be noted from FIG. 7, the injector for the internal combustion engine wherein the valve is actuated by the electromagnet causes a significant length of ineffective time to be consumed between start of flowing of an electric current through the exciting coil and actual opening of the valve. Thus, fuel injection is delayed until time t1 or t2 at which the valve is rendered open elapses after the exciting coil is fed with electricity. Thus, of the signal width Tj of the injection command signal, a period of time between start of flowing of the exciting current Id through the exciting coil and actual opening of the valve of the injector is ineffective time Tm and a period of time during which the valve is kept open is effective time Ta.
The ineffective time Tm is increased with a decrease in driving voltage Vd. In order to accurately control a feed rate of fuel fed to the internal combustion engine, it is required to minimize a variation of the ineffective time Tm to a variation of the driving voltage Vd. Unfortunately, the convention fuel injection equipment causes the ineffective time Tm to be substantially varied with respect to the driving voltage Vd. Thus, in order to permit accuracy of the injector to be within a tolerance, it is required to arrange a voltage detection circuit 8 for detecting the driving voltage Vd to correct the signal width Tj (=Tm+Ta) of the injection command signal Vj depending on an output of the voltage detection circuit 8.
In the conventional fuel injection equipment shown in FIG. 5, the injector 1 is so constructed that rising of the exciting current Id is relatively delayed and a saturation value thereof is relatively low, so that it is not required to carry out control for restricting a magnitude of the exciting current Id. However, such an injector causes the ineffective time Tm to be increased, resulting in a variation in ineffective time Tm to a variation in driving voltage Vd being increased.
On the contrary, when an injector wherein rising of the exciting current is rapid and a saturation value thereof is increased is incorporated in a fuel injection equipment, the ineffective time Tm is relatively reduced and a variation in ineffective time Tm to a variation in driving voltage Vd is reduced.
FIG. 8 shows another conventional fuel injection equipment for an internal combustion engine in which such an injector as described above wherein rising of the exciting current Id is rapid is incorporated. The fuel injection equipment is so constructed that a resistor 3b for current detection is connected in series to a collector-emitter circuit of a transistor constituting a switch circuit 3a of an injector driving circuit 3 and a current detection signal Vi produced across the resistor 3b is fed to a current control circuit 3c.
The current control circuit 3c functions to flow a current through a base of a transistor Tr to turn on the transistor when it is fed with an injection command signal Vj. Also, it functions to limit a magnitude of a current fed to the base of the transistor Tr to hold the exciting current Id at a constant holding current Ido when the current detection signal Vi reaches a set value Ido. The holding current Ido required for permitting a valve of the injector which has been rendered open to be kept open may be set to be a value lower than a maximum value of the exciting current generated prior to opening of the valve.
FIG. 9 shows a variation in exciting current Id with time in the fuel injection equipment shown in FIG. 8. In FIG. 9, curves a and b indicate characteristics obtained when the driving voltage Vd is Vd1 and Vd2 (&lt;Vd1), respectively. Also, in FIG. 9, t1' indicates time at which the valve of the injector is rendered open when the driving voltage Vd is Vd1 and t2' indicates time at which the valve is open when the voltage Vd is Vd2.
As will be noted from FIG. 9, even when the injector wherein rising of the exciting current is rapid and the ineffective time Tm is relatively reduced is incorporated in the fuel injection equipment, a variation of the ineffective time Tm to the driving voltage Vd is likewise relatively increased, so that it is still required to correct the fuel injection time Tj (=Tm+Ta) depending on the driving voltage Vd detected.
As described above, the conventional fuel injection equipment causes the ineffective time Tm between feeding of the injection command signal and actual opening of the valve to be substantially varied when the driving voltage Vd of the injector is varied. Thus, in order to accurately control a feed rate of fuel fed to the internal combustion engine, it is required to correct the signal width Tj of the injection command signal Vj with respect to the driving voltage Vd. Unfortunately, this requires a complicated operation for the correction, to thereby cause a time length for the correction to be substantially increased.
Also, when any ripple is contained in the driving voltage Vd in the case that the driving voltage Vd is to be detected for correction of the signal width Tj, a value of the voltage detected is caused to be varied depending on a timing at which the voltage is detected, resulting in the quantity of correction being varied, leading to a failure in accurate correction.
It would be considered that a battery of an increased capacity is used to reduce the ripple of the driving voltage. Unfortunately, such a battery causes a weight of the internal combustion engine to be significantly increased to a degree sufficient to deteriorate a fuel consumption rate of the engine.
Further, it would be considered that a smoothing capacitor is connected to a circuit for detecting the driving voltage to eliminate the ripple. However, connection of the smoothing capacitor deteriorates responsibility of the equipment.
Moreover, averaging of a detection value of the driving voltage would be considered for sampling. However, this likewise deteriorates the responsibility.